The present invention relates to diffractive optical systems having image forming capability, and particularly to a diffractive optical imaging lens system which is corrected for aberrations.
1. Field of the Invention
The invention is especially suitable for use as a landscape lens as well as a lens having finite conjugates and provides imaging with monochromatic illumination. The invention also provides an f-theta scan lens useful in laser scanners. The diffractive lens is preferably of zone plate configuration which can be stamped or pressed in a medium transparent to the illumination, such as plastic. The lens may also be a holographic element, either optically recorded or computer-generated.
2. Description of the Related Art
Diffractive optical elements have not been used for imaging since they produce unacceptably large amounts of image aberration except in the immediate vicinity of the optical axis. Reference may be had to the following patents and publications for further information respecting diffractive lenses, and particularly hologram lenses: G. P. Sincerbox, "Formation of Optical Elements by Holography", IBM Tec. Disclosure Bull, 10, 267 (1967); Brooks et al., U.S. Pat. No. 3,578,845 of May 18, 1971; Tatsuno et al., U.S. Pat. No. 4,688,880, Aug. 25, 1987; Kuwayama et al., U.S. Pat. No. 3,626,679, Dec. 2, 1986; Withrington, U.S. Pat. No. 3,940,204, Feb. 24, 1976; Antonson et al., U.S. Pat. No. 3,737,212, June 5, 1973; Tien, U.S. Pat. No. 4,140,362, Feb. 20, 1979; and Bjorklund et al., U.S. Pat. No. 4,432,597, Feb. 21, 1984. It has been proposed to correct a diffractive optical element for phase errors thereby providing a corrected Fourier-transform lens. See J. Kedmi and A. A. Friesem, "Optimal Holographic Fourier-Transform Lens", Applied Optics, 23, 22, 4015-4019 (15 Nov. 1984); and J. N. Cederquist and J. R. Fienup, "Analytic Design of Optimum Holographic Optical Elements", J. Opt. Soc. Am. A, 4, 4, 699-705 (April 1987). Diffractive optical elements have, however, not been considered useful for imaging of objects (as contrasted with conventional glass lenses) because of the large amounts of aberration introduced by the diffractive lens in the image plane.